Water thinnable coating compositions have become of increasing importance in everyday life in various types of industrial applications because of ease in application and clean-up. Such water soluble compositions are increasingly desirable because of environmental considerations as a minimal amount of organic solvent is released to the atmosphere both in manufacture and use. Various types of aqueous coating systems have been used in the art and have greatly facilitated the application and clean-up and have obviated the use of turpentine or similar types of organic thinners.
Two component water dispersible coatings employing epoxy resins have been used in the art employing polyamide in a curing agent non-acid system. Such systems do not entail any significant problem of flash-rusting of ferrous metal substrates. There have been recently developed water base coatings exhibiting improved applications and film properties such as tack-free drying, better coating properties and color utilizing acidified aminoethylated interpolymer curing agents for epoxy resins. Such curing agents are described in R. T. McFadden U.S. Pat. No. 3,634,372 granted Jan. 11, 1972 and are further shown in water thinnable coating compositions using the curing agent in Martin et al U.S. Pat. No. 3,719,629 granted Mar. 6, 1973. Both patents are assigned to The Dow Chemical Company.
Such coating compositions employing the acidified aminoethylated interpolymer with an epoxy resin although exhibiting quite desirable film or coating characteristics show undersirable properties when used on steel substrates in the development of flash-rusting. This is believed to be because an acid is used to neutralize the aminoethylated interpolymer causing a bronze tone or flash-rusting to be developed when the coating is applied to the steel substrate. The discoloration or flash-rusting is unsightly and undesirable and shows through top coating with white pigments and other color.